@deftypefun {int} {gnutls_dtls_cookie_send} (gnutls_datum_t * @var{key}, void * @var{client_data}, size_t @var{client_data_size}, gnutls_dtls_prestate_st * @var{prestate}, gnutls_transport_ptr_t @var{ptr}, gnutls_push_func @var{push_func})
@var{key}: is a random key to be used at cookie generation

@var{client_data}: contains data identifying the client (i.e. address)

@var{client_data_size}: The size of client's data

@var{prestate}: The previous cookie returned by @code{gnutls_dtls_cookie_verify()} 

@var{ptr}: A transport pointer to be used by  @code{push_func} 

@var{push_func}: A function that will be used to reply

This function can be used to prevent denial of service
attacks to a DTLS server by requiring the client to
reply using a cookie sent by this function. That way
it can be ensured that a client we allocated resources
for (i.e. @code{gnutls_session_t} ) is the one that the 
original incoming packet was originated from.

This function must be called at the first incoming packet,
prior to allocating any resources and must be succeeded
by @code{gnutls_dtls_cookie_verify()} .

@strong{Returns:} the number of bytes sent, or a negative error code.  

@strong{Since:} 3.0
@end deftypefun